Reduction of cavitation in fuel pumps

ABSTRACT

A fluid gear pump gear arranged to rotate about a first axis. The fluid gear pump gear includes a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first hub portion and the first teeth being coated with a vapor-deposited of cavitation resistant coating. The gear also includes a first shaft on which the first hub portion is carried.

BACKGROUND

The subject matter disclosed herein generally relates to the field of fuel pumps, and more particularly to an apparatus and method for reducing cavitation in fuel pumps.

Aircraft gas turbine engines receive pressurized fuel from different kinds of fuel pumps including gear-type fuel pumps. The gear pump typically performs over a wide operational speed range while providing needed fuel flows and pressures for various engine performance functions.

Gear pumps often comprise two coupled gears of similar configuration and size that mesh with each other inside an enclosed gear housing. A drive gear may be connected rigidly to a drive shaft. As the drive gear rotates, it meshes with a driven gear thus rotating the driven gear. As the gears rotate within the housing, fluid is transferred from an inlet to an outlet of the gear pump. Typically, the drive gear carries the full load of the gear pump drive or input shaft. The two gears may operate at high loads and high pressures, which may stress the gear teeth.

For given gear sizes the volume of fluid pumped through the gear pump may partially depend on the geometry of the tooth (e.g., depth, profile, etc.), the tooth count, and the width of the gear. Most gear pumps have gears with about ten to sixteen teeth. As the gears rotate, individual parcels of fluid are released between the teeth to the outlet. A common problem with more traditional gear pumps operating at high rotational speeds is cavitation erosion of the surfaces of the gear teeth and bearings. Cavitation erosion results in pitting of surfaces of the gear teeth that may eventually result in degraded pump volumetric capacity and affect pump operability and durability.

BRIEF SUMMARY

According to one embodiment, will track claims a fluid gear pump is disclosed. The pump includes a first gear constructed and arranged to rotate about a first axis, the first gear including a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first teeth being coated with a vapor-deposited of cavitation resistant coating. The pump also includes a second gear operably coupled to the first gear for rotation about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion. At a time in operation the plurality of first teeth and the plurality of second teeth contact at first contact point and a second contact point to create a backlash volume interposed between the first contact point and the second contact point. The pump also includes a first bearing abutting and coaxial to the first hub portion; and a second bearing abutting and coaxial to the second hub portion.

In any prior embodiment, the coating is deposited by filter arc deposition.

In any prior embodiment, the coating is a nickel titanium (NiTi).

In any prior embodiment, the coating is deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD).

In any prior embodiment, the coating is at least one of titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride or a tungsten containing material.

In any prior embodiment, the coating is a diamond-like carbon

In any prior embodiment, the pump further includes a first shaft on which the first gear is carried, and a second shaft on which the second gear is carried. In this embodiment. The second gear is also coated with the vapor-deposited of cavitation resistant coating.

In any prior embodiment, the pump further includes a third gear carried on the second shaft.

In any prior embodiment, one or more of the first, second and third gears include a nickel titanium coating thereon.

In one embodiment, a method of reducing cavitation during fluid gear pump operation is disclosed. The method includes: rotating a first gear around first axis, the first gear including a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, wherein the first teeth are coated with a vapor-deposited of cavitation resistant coating; rotating a second gear coupled to the first gear about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein the plurality of first teeth engage the plurality of second teeth; and transferring fluid from a low pressure side to a high pressure side when the first gear is rotating and the second gear is rotating.

In any prior method, wherein the first gear is coated with nickel titanium.

In any prior method, the first gear is coated with one of: titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride, tungsten or tungsten carbide, or a diamond-like carbon.

In one embodiment, a fluid gear pump gear arranged to rotate about a first axis is disclosed. The fluid gear pump gear includes a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first hub portion and the first teeth being coated with a vapor-deposited of cavitation resistant coating; and a first shaft on which the first hub portion is carried.

The fluid gear pump gear of any prior embodiment, wherein the first gear is coated with nickel titanium.

The fluid gear pump gear of any prior embodiment, wherein the first gear is coated with one of: titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride, tungsten or tungsten carbide, or a diamond-like carbon.

The fluid gear pump gear of any prior embodiment, further comprising a second gear carried on the first shaft.

The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, that the following description and drawings are intended to be illustrative and explanatory in nature and non-limiting.

BRIEF DESCRIPTION

The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 illustrates a schematic of an aircraft fuel system as one, non-limiting, example of an application of a gear pump of the present disclosure;

FIG. 2 illustrates a perspective view of the gear pump with a housing removed to show internal detail;

FIG. 3 shows a side view of the drive and driven gears of the gear pump;

FIG. 4 is a perspective view of a portion of a gear according to one or more embodiments; and

FIG. 5 is a cross-sectional view of a tooth of FIG. 4.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

Various embodiments of the present disclosure are related to the reduction of fluid cavitation within gear pumps. Aircraft engine high pressure fuel pumps typically use a pair of involute gears to generate fuel pressure for the burner injectors. These gears are enclosed in a housing within which they are supported by bearings. In the vicinity of the gear meshing region these bearings form a bridgeland that separates the high and low pressure regions and maintains high pump efficiency. A pump of this description experiences significant pressure oscillations that may lead to the formation and subsequent collapse of cavitation bubbles that may cause material damage. The gears may be especially susceptible to cavitation damage and that results in a deterioration of pump performance and can significantly reduce the useable life of these components.

To address these issues a gear shaft that includes gear teeth coated with a cavitation resistant coating. Utilization of such a coating for the gears generally and gear teeth in particular may have the technical effect of reducing cavitation on the gear teeth. Non-limiting examples of such coatings include NiTi (nickel titanium) applied by filtered arc deposition, physical vapor deposition (PVD) or chemical vapor deposition (CVD) applied coatings, such as titanium nitride, titanium aluminium nitride (TiAlN), or titanium aluminum silicon nitride, tungsten or tungsten carbide, or diamond-like carbon, or high velocity oxygen fuel (HVOF)-sprayed carbidethermal spray powders such as WC-10Co-4Cr. In some embodiments, only a portion of a gear tooth may include a coating and the rest formed of another material, such as stainless steel.

Referring to FIG. 1, one embodiment of a fuel system 20 of the present disclosure is illustrated. The fuel system 20 may be an aircraft fuel system and may include a fuel supply line 22 that may flow liquid fuel from a fuel tank 24 to fuel nozzles 26 of an engine (not shown). A fuel bypass line 28 may be arranged to divert fuel from the supply line 22 and back to the fuel tank 24. Various fuel system components may interpose the fuel supply line 22 and may include a low pressure fuel pump 30, a heat exchanger 32, a fuel filter 34, a high pressure fuel pump 36, a metering valve 38, a high pressure fuel shutoff valve 40, a screen 42, a fuel flow sensor 44, and a fuel tank shutoff valve 45. The low pressure fuel pump 30 may be located downstream of the fuel tank 24. The heat exchanger 32 may be located downstream of the low pressure fuel pump 30. The fuel filter 34 may be located downstream of the heat exchanger 32. The high pressure fuel pump 36 may be located downstream of the fuel filter 34 and upstream of the fuel bypass line 28. The metering valve 38 may be located downstream from the bypass line 28. The high pressure fuel shutoff valve 40 may be located downstream from the bypass line 28. The screen 42 may be located downstream from the high pressure fuel shutoff valve 40, and the fuel flow sensor 44 may be located downstream from the screen 42. It is further contemplated and understood that other component configurations of a fuel system are applicable and may further include additional sensors, valves and other components.

The heat exchanger 32 may be adapted to use the flowing fuel as a heat sink to cool other liquids flowing from any variety of auxiliary systems of an aircraft and/or the engine. For example, the heat exchanger 32 may transfer heat from an oil and to the fuel. The oil may be used to lubricate any variety of auxiliary components including, for example, a gear box (not shown) of the engine. Such a transfer of heat may elevate the temperature of the fuel which may make the high pressure fuel pump 36 more prone to cavitation.

Referring to FIGS. 2 and 3, one non-limiting example of the high pressure fuel pump 36 is illustrated as a gear pump with a housing removed to show internal detail. The housing is shown, generally, by dashed line 61.

The gear pump 36 may be a dual stage pump and may include an fuel centrifugal boost pump housing 46, an input drive shaft 48 constructed for rotation about a first axis 50, a coupling shaft 52 constructed for rotation about a second axis 54, a drive gear 56 with associated bearings 58, a driven gear 60 with associated bearings 62, a motive drive gear 64 and a motive driven gear 66 configured for rotation about a third axis 68. The axis 50, 54, 68 may be substantially parallel to one-another. The drive shaft 48 may attach to an engine gear box (not shown). The drive gear 56 is engaged and concentrically disposed about the drive shaft 48. The driven gear 60 and motive drive gear 64 are engaged and concentrically disposed about the coupling shaft 52.

The drive and driven gears 56, 60 are rotationally coupled to one another for the pumping (i.e., displacement) of fuel as a first stage, and the motive drive gear 64 and motive driven gear 66 are rotationally coupled to one another for the continued pumping of the fuel as a second stage.

In one embodiment, some or all of at least one of the drive gear 56 and the driven gear 60 is coated with a coating as described herein. In one embodiment, all of the one or both of the drive or driven gears 56, 60 are formed of a so coated. In another, only the teeth are coated and in yet another, only a portion of one or more of the teeth is coated. As discussed above, examples of suitable coatings include NiTi applied by filtered arc deposition, PVD or CVD applied coatings, such TiN, TiAlN, TiAlSiN, tungsten or tungsten carbide or diamond-like carbon, or high velocity oxygen fuel (HVOF)-sprayed carbide thermal spray powders such as WC-10Co-4C. The same may also apply to the motive drive and motive driven gears 64, 66.

It is further contemplated and understood that many other types of gear pumps may be applicable to the present disclosure. For example, the gear pump may be a single stage gear pump, and/or the drive shaft 48 may be attached to any other device capable of rotating the drive shaft 48 (e.g., electric motor).

The bearings 58, 62 may be inserted into a common carrier 70 that generally resembles a figure eight. A gear bearing face geometry, known in the art as a bridgeland 100 may be sculpted to minimize cavitation and pressure ripple that may deteriorate the integrity of the pump components, discussed further below. The bridgeland 100 separates a low pressure side and a high pressure side of the pump.

In operation, the gear pump 36 is capable of providing fuel at a wide range of fuel volume/quantity and pressures for various engine performance functions. The engine gearbox provides rotational power to the drive shaft 48 which, in-turn, rotates the connected drive gear 56. The drive gear 56 then drives (i.e., rotates) the driven gear 60 that rotates the coupling shaft 52. Rotation of the coupling shaft 52 rotates the motive drive gear 64 that, in-turn, rotates the motive driven gear 66.

FIG. 4 shows a perspective view of a gear. The gear can be any of the drive gear 56, the driven gear 60, the motive drive gear 64 and the motive driven gear 66. Referring to FIG. 4, each of the gears 56, 60, 64, 66 may include a hub portion 72 and a plurality of teeth 74 that may both span axially between two opposite facing sidewalls 76, 78. Each sidewall 76, 78 may lay within respective imaginary planes that are substantially parallel to one-another. The hub portion 72 may be disc-like and projects radially outward from the respective shafts 48, 52 and/or axis 50, 54, 68 to a circumferentially continuous face 80 generally carried by the hub portion 72. The face 80 may generally be cylindrical. The plurality of teeth 74 project radially outward from the face 80 of the hub portion 72 and are circumferentially spaced about the hub portion 72. The gears 56, 60, 64, 66 may be spur gears, helical gears or other types of gears with meshing teeth, and/or combinations thereof.

The hub portion 72 can be coated in one embodiment. In such an embodiment, the spaces between the teeth 74 (shown by reference numeral 75) may be coated. The coating can include any of the coatings disclosed herein or other suitable coatings.

A suitable coating will have, in one embodiment, a high hardness of over 9 GPa. Such coatings may optionally also have an elasticity of greater than 100 GPa on stainless steels.

In another embodiment, the hub portion 72 is formed of metal, such as steel or stainless steel and the teeth 74 are coated while the hub is not.

FIG. 5 shows a cross-section taken along lines 5-5 of FIG. 4. The exemplary tooth 74 includes a base 77 that can formed of steel or stainless steel and, in one embodiment, if formed of the same material as the hub portion 72 (FIG. 4). The base 77 can also be called a tooth or tooth portion herein. The base is coated with a coating 79. The coating can be any of the coatings discussed herein. In one embodiment, the coating is applied at a thickness (t) of less than 5 micrometers.

The term “about” is intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof.

While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims. 

What is claimed is:
 1. A fluid gear pump comprising: a first gear constructed and arranged to rotate about a first axis, the first gear including a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first teeth being coated with a vapor-deposited of cavitation resistant coating; a second gear operably coupled to the first gear for rotation about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein at a time in operation the plurality of first teeth and the plurality of second teeth contact at first contact point and a second contact point to create a backlash volume interposed between the first contact point and the second contact point; a first bearing abutting and coaxial to the first hub portion; and a second bearing abutting and coaxial to the second hub portion.
 2. The fluid gear pump as set forth in claim 1, wherein the coating is deposited by filter arc deposition.
 3. The fluid gear pump as set forth in claim 2, wherein the coating is nickel titanium (NiTi).
 4. The fluid gear pump as set forth in claim 1, wherein the coating is deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD).
 5. The fluid gear pump as set forth in claim 4, wherein the coating is at least one of titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride or a tungsten containing material.
 6. The fluid gear pump as set forth in claim 1, wherein the coating is a diamond-like carbon
 7. The fluid gear pump set forth in claim 1, further comprising: a first shaft on which the first gear is carried; and a second shaft on which the second gear is carried; wherein the second gear is coated with the vapor-deposited of cavitation resistant coating.
 8. The fluid gear pump as set forth in claim 7, further comprising a third gear carried on the second shaft.
 9. The fluid gear pump as set forth in claim 8, wherein one or more of the first, second and third gears include a nickel titanium coating thereon.
 10. A method of reducing cavitation during fluid gear pump operation, the method comprising: rotating a first gear around first axis, the first gear including a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, wherein the first teeth are coated with a vapor-deposited of cavitation resistant coating; rotating a second gear coupled to the first gear about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein the plurality of first teeth engage the plurality of second teeth; and transferring fluid from a low pressure side to a high pressure side when the first gear is rotating and the second gear is rotating.
 11. A method as set forth in claim 10, wherein the first gear is coated with nickel titanium.
 12. A method as set forth in claim 11, wherein the first gear is coated with one of: titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride, tungsten or tungsten carbide, or a diamond-like carbon.
 13. A fluid gear pump gear arranged to rotate about a first axis, the fluid gear pump gear comprising: a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first hub portion and the first teeth being coated with a vapor-deposited of cavitation resistant coating; and a first shaft on which the first hub portion is carried
 14. The fluid gear pump gear of claim 13, wherein the first gear is coated with nickel titanium.
 15. A fluid gear pump gear of claim 13, wherein the first gear is coated with one of: titanium nitride, titanium aluminium nitride (TiAlN), titanium aluminum silicon nitride, tungsten or tungsten carbide, or a diamond-like carbon.
 16. The fluid gear pump gear as set forth in claim 15, further comprising a second gear carried on the first shaft. 